Three-layer stencil assembly having plastic overlay sheet

ABSTRACT

There is disclosed an improvement in the mimeograph stencil art comprising the manufacture of an overlay sheet for either a conventional typewriter stencil or in particular a stencil which can be prepared by means of heat transfer with a thermocopier and with this overlay sheet is capable of either thermal production or conventional typewritten production, comprising a sheet of tissue which has been coated on one side, only, with a film of elastomeric plastic, such as polyvinyl chloride or polypropylene.

limited States Patent Inventor Herbert P. Sherman Chicago, Ill.

Appl. No. 800,972

Filed Feb. 20, 1969 Patented July 27, 1971 Assignee Bell 8: HowellCompany Chicago, 111.

THREE-LAYER STENCIL ASSEMBLY HAVING PLASTIC OVERLAY SHEET 10 Claims, 6Drawing Figs.

U.S.Cl 101/1282, 1l7/35.5,117/135,117/155,161/149,161/156, l6l/160,161/235, 161/249, 161/251, 161/256 lnt.Cl B4111 1/24 FieldoiSearch161/113, 254, 218, 241, 247, 251, 256,149,156,166, 235; 117/355, 35.6,36.1, 38, 36.7, 36.8, 36.9,135, 155;]01/1282, l27,128,128.1,128.3,128.4;

[Mm Aria [56] References Cited UNITED STATES PATENTS 1.092,768 4/1914Fuerth..... 101/1282 2,203,280 6/1940 Heath 101/1282 3,009,416 11/1961Frasher etal. 101/1282 3,062,675 11/1962 Shelffo 117/355 3,376,8104/1968 Blake etal. 117/35.5

FORElGN PATENTS 446,018 1/1948 Canada 101/1282 Primary Examiner-John T.Goolkasian Assistant Examiner-W. E. Hoag Attorney-Jack H. Hall Jam 46667 THREE-LAYER STENCIL ASSEMBLY HAVING PLASTIC OVERLAY SHEET FIELD OFTHE INVENTION The present invention relates generally to improvements inthe mimeograph stencil art and more particularly to a new and improvedstencil assembly wherein the stencil is capable of being prepared bymeans ofa thermocopier and by means ofa conventional typewriter.

DESCRIPTION OFTHE PRIOR ART One of the most critical problems concerningdesigners of mimeograph stencils has been the problem of designing astencil which can be prepared by means of a thermocopier or byconventional typing. This problem is overcome by the present invention.To completely understand the instant invention it is necessary tooutline the prior art stencils that are available and to describe theirdifferences.

Broadly, there are four types of mimeograph stencils: One is prepared bythe use of a typewriter or a blunt pointed instrument referred to as astylus. A second can be prepared by means of a photographic system,whereby a sheet ofcmulsion coated tissue is exposed photographically andthe blacks on the emulsion are eliminated chemically leaving exposedapertures. A third type is prepared by the use of an electronic scanningdevice which burns tiny apertures into a plastic sheet. The fourth andnewest type, referred to as a thermal stencil, is prepared with athermocopier. Referring now to the conventional typing stencils, thereis shown in FIG. I a typical prior art typing stencil whichvconsists oftwo sheets, a first backing sheet which is made of a heavy althoughflexible paper much like that from which postcards are made, and secondsheet which is the stencil layer and is made by coating or impregnatinga sheet of fine fibered tissue paper with a film of highly plasticizedmaterial, such as nitrocellulose on both sides or it can even be coatedinstead with wax. Fig. 2 shows a modification of the conventional typingstencil wherein a clear plastic overlay is placed on top of the stencillayer sheet. Openings which would represent alphabetical letters, numerals, or drawn lines are made in this waxlike coating by striking thiscoating or if an overlay is present, by striking this overlay with thetype face ofa typewriter key. In either case, no part of the waxlikecoating is actually removed. It is merely pushed" to the outer edges ofthe holes or aperture made by the typewriter or the stylus. With theadvent of electric typewriters however, the conventional stencil hassuffered from what is commonly referred to as chop-outs. This means thatthe center of the 0," a, e," etc. can be actually cut out and therebydestroy the perfection of the stencil. There are actually two reasonsfor this: first, because the force of the strike by the typewriter notonly pushes aside the waxlike coating, but also cuts the fibers of thetissue; and second, because most plasticizers used for coating thestencil sheet have a pH rating on the acid side and, after a time andexposure to oxygen, the tissue fibers become brittle and thus break veryeasily. While the conventional clear plastic overlay shown in FIG. 2primarily accomplishes the function of preventing "chop-outs" it doesnot overcome the problem existing in pushing" the wax material to theside of the letters thereby causing a broader aperture. Therefore, thecurrent clear plastic overlaid stencils prepared by typewriter do notyield an image as clear and sharp as desired without chopouts."

The other type of stencil to which this invention relates is the thermalstencil. Shown in FIG. 3 is the most popular type of thermal stencilknown in the trade as the Weber stencil." This stencil comprises aconventional backing sheet of flexible oil resistant paper. Attached tothis backing sheet is a plasticized plastic coated tissue stencil sheet.Attached to this layer is a tissue layer which in thermal stencil makingacts as a receptor sheet. The original sheet which is to be copied isplaced face up between the backing sheet and the plasticized plasticcoated tissue stencil sheet. The entire sandwich combination is placedinto a thermocopier and through heat transfer the latent image appearson the stencil sheet represented by aperturesjust as ifit had beenaccomplished by typewriting. This because the overlay of plain tissue,acting as a receptor, absorbs the plasticized plastic coating which hasbeen melted away, so to speak, at the point of contact between thecoating and the latent image. This Weber stencil can also be used as atypewriter stencil. The typing is done either on the tissue or directlyon the coated sheet layer but the force of the keys in either case canmake holes in the middle stencil layer representative of the letters.However, a great deal of chop-outs as well as pushing" as describedabove in the conventional typing stencils is present and the suitabilityof this stencil for typewritten preparation is limited. A second type ofthermostencil known to the prior art is shown in FIG. 4. This stencil isknown as the Riso stencil. The stencil is a two-layer stencil consistingof a conventional backing sheet attached to a second sheet which is atissue having a laminated plastic coating of unknown composition on theunder side thereof and forms the stencil sheet. The operation of thisstencil is similar to that of the Weber stencil" described above. Thisstencil cannot be prepared by a typewriter however. A third type ofthermal stencil is available and operates in a similar manner to theabove two stencils. This stencil, known as the American stencil," isconstructed similarly to the Weber stencil; however the stencil sheetutilizes a different type of coating. This stencil is also incapable ofbeing prepared with a typewriter and can only be used in conjunctionwith a thermocopying device. Needless to say, the typewriter stencilshown in FIGS. 1 and 2 cannot be used with a heat transfer process.

SUMMARY OF INVENTION The general purpose of this invention is to providea stencil which embraces all the advantages of similarly employedstencils and possesses none of the aforedescribed disadvantages. Toattain this, the present invention contemplates a unique arrangementwhereby a sheet of tissue, coated on one side only with a film ofelastomeric plastic, such as polyvinyl chloride, or polypropylene, isused as an overlay on either a conventional typing stencil as shown inFIG. I or instead of the overlay sheet or receptor on what is known asthe Weber stencil as shown in FIG. 3. This plastic coated tissue sheetwhich is used as an overlay on these two stencils provides a uniquesingle stencil which is capable of being prepared with a typewriter orwith a thermocopier and providing a clear aperturc which does notcontain cutouts and does not employ pushing" of the coated stencilmaterial to form this aperture but rather absorbs it.

It is therefore an object of the present invention to provide a stencilwhich is capable of being prepared by a typewriter or by a thermocopier.

Another object is to provide a typewriter stencil which does not havecutouts" and whose apertures are not formed by pushing the coatedstencil material aside.

A further object of the invention is to provide a stencil which isinexpensive to manufacture and which provides im proved results.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 5 is a diagrammatic viewillustrating a preferredembodiment ofthe invention when utilized with athermostencil.

FIG. 6 is a diagrammatic view illustrating a second embodiment of theinvention when utilized with a conventional typewriter stencil.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingswherein like reference characters designate like or corresponding partsthroughout the several views, there is shown in FIG. 5, whichillustrates a preferred embodiment, a stencil assembly ll capable ofbeing prepared by either thermocopying or by conventional typewriting.The stencil assembly is a three-layer stencil having a backing layer 13.a stencil layer 14, and a coated overlay layer 17 and in some respectsis similar to the stencil shown in FIG. 3 and described as the priorart. Backing sheet 13 is conventional and is made from a sheet of heavyflexible paper. Fastened to backing sheet 13 along a line 20 is thestencil layer 14 consisting of a tissue layer 15 coated with a plasticsubstance l6. Attached to this sandwich along the line is the overlaysheet 17 consisting ofa tissue 18 coated with a film of elastomericplastic 19 on its uppermost side. While any elastomeric plastic such aspolyvinyl chloride or polypropylene may be used, polyvinyl chloride ispresently preferred. Layer 17 gives the stencil the capability of bothbeing a thermostencil and a conventional typewriter stencil. This layeracts as both a cushion sheet and an absorbing receptor layer. When atypewriter is utilized for preparing the stencil, this layer preventschop-outs due to the plastic surface 19 and prevents pushing" of thestencil plastic coating material due to tissue layer 18 actuallyabsorbing the plastic material from stencil layer 14 thereby providing aclean aperture.

A further result of providing the cushioning sheet with the plastic film19 is evident when this same stencil assembly is used as athermostencil; a more uniform coating 16 and consequently, a cleaner andsharper aperture in stencil sheet 14 is achieved. One reason for thisoccurrence is the fact that a great concentration of heat is transferredto the stencil sheet at the points of contact between the characters onthe original and the coated stencil layer when the plastic film ispresent than with the, previously referred to, prior art stencils.

Now referring to FIG. 6, which constitutes an alternative embodiment,there is shown a typewriter stencil assembly 21 wherein an elastomericplastic coated overlay 17 is placed on a conventional typing stencilsuch as that shown in FIG. 1. The stencil assembly comprises a backinglayer 13 connected to a stencil sheet 23 which is comprised of either awax or cellulose coating 25 placed upon a tissue layer 24, the stencilsheet and backing sheet being fastened together along a line 20 in aconventional manner. Also attached along line 20 is the coated overlay17 which, as described above in connection with FIG. 5, is made up of atissue layer 18 and an elastomeric plastic coating 19 laminated thereto.As described with reference to the prior art, the conventional typingstencils shown in FIG. I suffer from the defect of having chop-outs" andfrom a pushing" effect of the wax stencil coating when struck by atypewriter key. By utilizing the overlay layer 17 these effects areeliminated. The elastomeric plastic coating 19 acts as a cushioninglayer for the typewriter keys thereby preventing chop-outs while tissuelayer 18 of the laminated structure absorbs the wax or cellulose coatingfrom stencil sheet 23 thereby preventing "pushing" of the stencilcoating material. This results in a clean aperture. This absorbentfeature is completely lacking in any of the prior art stencils.

While the results obtained from utilizing this elastomeric plasticlaminated overlay appear deceptively simple, it is to be emphasized thatthe use of this overlay layer now provides a stencil assembly which iscapable of both preparation by conventional typing means or by means ofa thermocopier. It further provides an absorbent tissue layer to removeany excess material from the stencil layer and gives a cushioning effectwhich prevents chop-outs." When the stencil sheet is prepared with athermocopier this elastomeric plastic coated overlay provides a highermelting temperature than previous overlays thereby absorbing morematerial from the stencil sheet. Even utilizing this layer with aconventional typing stencil as shown in FIG. 6 an improved result isobtained by providing a cushioning layer as an absorbing layer therebypreventing chop-outs and pushing effects which have previously not beenaccomplished. It should be understood, of course, that the foregoingdisclosure relates to only preferred embodiments of the invention andthat numerous modifications or alterations may be made therein withoutdeparting from the spirit and the scope ofthe invention as set forth inthe appended claims.

What I claim is:

l. A mimeograph stencil assembly having a sandwiehlike constructioncomprising:

a first sheet;

a second sheet positioned on said first sheet wherein said second sheetcomprises a stencil layer; and

a third sheet comprising a tissue layer having an elastomeric plasticfilm coated on one side thereof and wherein the uncoated side of saidtissue layer is placed adjacent to and facing said stencil layer.

2. A mimeograph stencil assembly as in claim 1, wherein:

said stencil layer comprises a tissue layer coated with a plasticizedplastic coating having a melting point lower than said elastomericplastic coating; and wherein said third sheet is adapted to absorb thecoating of said stencil layer thereby forming apertures in said stencillayer upon the application of heat or pressure thereto.

3. The mimeograph stencil assembly of claim 2 wherein said third layeris adapted to provide a cushioning effect thereby protecting saidstencil layer from excessive pressure being applied thereto.

4. A mimeograph stencil assembly as in claim 1, wherein:

said second sheet comprises a tissue layer coated with plasticizedmaterial; and wherein said third sheet is adapted to absorb the coatingof said stencil layer thereby forming apertures in said stencil layerupon the application of pressure thereto and wherein said third sheetfurther is adapted to provide a cushioning ef fect thereby protectingsaid stencil layer from excessive pressure being applied thereto.

5. The mimeograph stencil assembly of claim 4 wherein said plasticizedcoating material said stencil layer is nitrocellulose. 6. A mimeographstencil assembly as in claim 1, wherein:

said stencil layer comprises a tissue layer coated with a waxlikematerial; and wherein said third sheet is adapted to absorb the coatingof said stencil layer thereby forming apertures in said stencil layerupon the application of pressure thereto and wherein said third sheetfurther is adapted to provide a cushioning ef fect thereby protectingsaid stencil layer from excessive pressure being applied thereto.

7. The mimeograph stencil assembly of claim 6 wherein said elastomericplastic film is polyvinyl chloride.

8. The mimeograph stencil assembly of claim 6 wherein said elastomericplastic film is polypropylene.

9. The mimeograph stencil assembly of claim 1 wherein said elastomericplastic film is polyvinyl chloride.

10. The mimeograph stencil assembly of claim 1 wherein said elastomericplastic film is polypropylene.

1. A mimeograph stencil assembly having a sandwichlike constructioncomprising: a first sheet; a second sheet positioned on said first sheetwherein said second sheet comprises a stencil layer; and a third sheetcomprising a tissue layer having an elastomeric plastic film coated onone side thereof and wherein the uncoated side of said tissue layer isplaced adjacent to and facing said stencil layer.
 2. A mimeographstencil assembly as in claim 1, wherein: said stencil layer comprises atissue layer coated with a plasticized plastic coating having a meltingpoint lower than said elastomeric plastic coating; and wherein saidthird sheet is adapted to absorb the coating of said stencil layerthereby forming apertures in said stencil layer upon the application ofheat or pressure thereto.
 3. The mimeograph stencil assembly of claim 2wherein said third layer is adapted to provide a cushioning effectthereby protecting said stencil layer from excessive pressure beingapplied thereto.
 4. A mimeograph stencil assembly as in claim 1,wherein: said second sheet comprises a tissue layer coated withplasticized material; and wherein said third sheet is adapted to absorbthe coating of said stencil layer thereby forming apertures in saidstencil layer upon the application of pressure thereto and wherein saidthird sheet further is adapted to provide a cushioning effect therebyprotecting said stencil layer from excessive pressure being appliedtherEto.
 5. The mimeograph stencil assembly of claim 4 wherein saidplasticized coating material said stencil layer is nitrocellulose.
 6. Amimeograph stencil assembly as in claim 1, wherein: said stencil layercomprises a tissue layer coated with a waxlike material; and whereinsaid third sheet is adapted to absorb the coating of said stencil layerthereby forming apertures in said stencil layer upon the application ofpressure thereto and wherein said third sheet further is adapted toprovide a cushioning effect thereby protecting said stencil layer fromexcessive pressure being applied thereto.
 7. The mimeograph stencilassembly of claim 6 wherein said elastomeric plastic film is polyvinylchloride.
 8. The mimeograph stencil assembly of claim 6 wherein saidelastomeric plastic film is polypropylene.
 9. The mimeograph stencilassembly of claim 1 wherein said elastomeric plastic film is polyvinylchloride.
 10. The mimeograph stencil assembly of claim 1 wherein saidelastomeric plastic film is polypropylene.